1. Field of the Invention
The present invention relates generally to a power control method in a wireless communication system for transmitting data wirelessly, and in particular, to a power control method in a wireless LAN (Local Area Network) system.
2. Description of the Related Art
In general, wireless communication systems are categorized into mobile communication systems and fixed wireless systems. A mobile communication system enables a user to communicate through a portable terminal while moving, whereas a fixed wireless communication system only allows the user terminal to communicate in while a fixed state. Although the fixed wireless system need not be fixed all the time, it must be situated at a fixed location during communication. WLL (Wireless Local Loop) and wireless LAN systems are examples of the fixed wireless systems. Fixed wireless communications occur usually within confines of a household. Fixed wireless systems are expected to account for a higher proportion of future wireless communication systems.
As described above, wireless access is usually made while the user is within confines of the household and a plurality of wireless terminals access a wired network via a wireless access node in the wireless communication system. In a mobile communication system, a mobile terminal is not confined to one particular node. As it roams, it is connected to varying nodes and accesses the wired network via these nodes. A typical mobile terminal carries a portable power supply such as a battery, to secure its mobility.
Due to the use of a portable power supply, such wireless terminals operate with limited power. Hence, a power mechanism for transmission/reception is significant to the wireless terminals. Meanwhile, the wireless access node is generally in a fixed location to receive power continuously. Therefore, power consumption does not concern the wireless access node and there is no particular need for power control for the wireless access node. That's why the transmit power of the wireless access node is almost fixed. However, if a plurality of households are engaged in wireless communication, excess transmit power of a wireless access node may interfere with the communication areas of other neighbor households. This will be a challenging issue as wireless terminals become widespread to common household use, especially as many wireless terminals are used in a narrow area like apartments. Moreover, if the wireless access node transmits more power than required, the power may leak to neighbors' wireless terminals.
This above described problem will be addressed in more detail with reference to FIG. 1. FIG. 1 illustrates deployment of a single wireless access point (AP) in each of the adjacent households and connection of a plurality of wireless terminals to each wireless AP. Referring to FIG. 1, a first AP 111 is located in a first home (home 1) and a second AP 121 in a second home (home 2). As stated earlier, these APs 111 and 121 transmit data with fixed power. Thus, the wireless coverage area of the first wireless AP 111, that is, the area in which access is enabled by a signal from the first wireless AP 111 reaches, is defined as denoted by reference numeral 110 and the wireless coverage area of the second wireless AP 121 is defined as denoted by reference numeral 120.
Given the coverage areas 110 and 120, a first wireless terminal 112 (wireless terminal 1) and a third wireless terminal 114 (wireless terminal 3), which communicate via the first wireless AP 111, are free of interference from other wireless APs. However, a second wireless terminal 113 (wireless terminal 2) covered by the first AP 111 experiences interference from the second wireless AP 121. A fourth wireless terminal 122 (wireless terminal 4) and a fifth wireless terminal 123 (wireless terminal 5), which communicate via the second AP 121, are free of interference from neighbor wireless APs. However, a sixth wireless terminal 124 (wireless terminal 6) covered by the second AP 121 experiences interference from the first wireless AP 111. The interference is attributed to the fixed transmit power of the wireless APs.
Less power from the second wireless AP 121 in home 2 is sufficient for data transmission. The same applies to home 1. As illustrated in FIG. 2, scaling down of the wireless coverage of the first AP 111 from an area 110a to an area 110b and the wireless coverage of the second AP 121 from an area 120a to an area 120b does not bring interference to signals from other wireless terminals. FIG. 2 illustrates a comparison between the actual coverage areas and optimum coverage areas of wireless APs. As noted from FIG. 2, it is necessary to adjust the transmit power of the wireless APs to such a level that it covers a minimum area sufficient to accommodate all authenticated terminals under a given wireless communication environment.
For this reason, APs with a power control function have been recently developed. However, the power control is performed by an operator's arbitrary setting, or its use is confined to adjustment of the cell area of a wireless AP in, for example, Europe. The conventional power control is not effective in adapting to an ambient environment or changes in the topology of wireless terminals.